Bragg reflection-based incident angle adaptive dual-band heat insulation composite film and preparation method thereof

Abstract

The application relates to the technical field of functional polymer film materials, and specifically discloses an incident angle adaptive double-waveband heat insulation composite film based on Bragg reflection and a preparation method thereof. The incident angle adaptive double-waveband heat insulation composite film based on Bragg reflection comprises a protective layer, an optical layer and an absorbing layer arranged in sequence, the optical layer is formed by alternately stacking a first resin material and a second resin material, the number of layers is not less than 100, the refractive indexes of the first resin material and the second resin material are different, a first reflection band is formed in a 360-450 nm waveband under a perpendicular incidence condition, and a second reflection band is formed in a 1100-1350 nm waveband; the reflection wavelength of the heat insulation composite film is blue-shifted with the increase of the incident angle, and the following conditions are met: Delta lambda vis / Delta theta >= 1 nm / degree, and Delta lambda IR / Delta theta >= 3 nm / degree. The application can overcome the defects of poor angle adaptability, single function and insufficient durability of the heat insulation film in the prior art.

Description

Technical Field

[0001] This application relates to the field of functional polymer thin film materials technology, and in particular to an incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection and its preparation method. Background Technology

[0002] With increasing demands for energy conservation and environmental protection, as well as enhanced visual comfort, window films that combine high-efficiency heat insulation with privacy protection are widely used in construction, automotive, and other fields. Currently, most commercially available heat insulation films are based on metal sputtering, ceramic coating, or single-medium multilayer film technologies, and their optical performance is typically optimized under perpendicular incidence conditions. For example, common metal-based heat insulation films block solar energy by forming a fixed reflective band in the near-infrared band, but its reflection band does not change with the incident angle, and its heat insulation performance is easily reduced due to the shift of the reflection band under oblique incidence. Furthermore, the metal layer suffers from problems such as easy oxidation, signal shielding, and visual abruptness. While ceramic-based heat insulation films have high infrared absorption rates, their absorption band is fixed, and they typically employ surface coating processes. Ceramic particles are susceptible to corrosion from environmental moisture and ultraviolet radiation, leading to performance degradation over time.

[0003] In recent years, multilayer film technology based on the Bragg reflection principle has been used to construct selective reflective films, achieving reflection control of specific wavelengths by alternately stacking materials with different refractive indices. However, existing films of this type are mostly designed for perpendicular incidence, where the center wavelength λ of the reflection band satisfies the relationship λ∝cosθ with the incident angle θ. When light is incident obliquely, the reflection band undergoes a blue shift. If the structure is not optimized to address this characteristic, it can cause a deviation from the target wavelength, reducing practical heat insulation performance. On the other hand, existing window films typically achieve visual privacy by adding dyes or maintaining low visible light transmittance, but their color often does not change with the viewing angle, failing to meet the needs of high light transmittance and dynamic privacy adjustment. Patent CN105954825A enhances infrared reflection by setting different metal reflective layers in the film layer, but its reflection band is fixed, lacking angle-adaptive characteristics, and it does not solve the problems of weather resistance and dynamic color adjustment with angle.

[0004] Therefore, developing a composite membrane that can automatically adjust its reflection band according to the angle of solar incidence to achieve efficient heat insulation, dynamic visual appearance adjustment, and excellent weather resistance has urgent market demand and technological significance. Especially for common oblique incidence scenarios such as automotive tilted windows and building curtain walls, collaborative innovation in material systems, membrane structures, and manufacturing processes is needed to overcome the shortcomings of existing technologies, such as poor angle adaptability, limited functionality, and insufficient durability. Summary of the Invention

[0005] To overcome the shortcomings of existing heat insulation films, such as poor angle adaptability, limited functionality, and insufficient durability, this application provides an incident angle adaptive dual-band heat insulation composite film based on Bragg reflection and its preparation method. This composite film can automatically adjust the reflection band according to the solar incident angle, achieving efficient heat insulation, angle-dependent color change, and excellent weather resistance.

[0006] In a first aspect, this application provides an incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection, employing the following technical solution: An incident angle adaptive dual-band heat insulation composite film based on Bragg reflection includes a protective layer, an optical layer, and an absorption layer arranged sequentially. The optical layer is formed by alternating stacking of a first resin material and a second resin material, with a stacking number of not less than 100 layers. The first resin material and the second resin material have different refractive indices to form a first reflection band in the 360-450nm band and a second reflection band in the 1100-1350nm band under vertical incident conditions. The reflected wavelength of the heat-insulating composite film undergoes a blue shift as the incident angle increases, and satisfies: Δλ vis / Δθ≥1nm / °,Δλ IR / Δθ≥3nm / °, where, Δλ vis Δλ is the wavelength change of the first reflection band. IR Δθ represents the wavelength change of the second reflection zone, and Δθ represents the change of the incident angle.

[0007] By adopting the above technical solution and using an alternating stacked structure of more than 100 layers, the dynamic matching of the incident angle θ and the reflected wavelength λ is achieved through the Bragg reflection equation: λ=2(n1d1+n2d2)cosθ. When θ increases from 0° to 60°, the infrared reflection band shifts from 1100-1350nm to 900-1150nm, accurately covering the band with the highest solar energy weighting coefficient (>80%) in the ASTM G173 standard, and the blue light band shifts from 400-450nm to below 380nm. By utilizing the angle sensitivity of the Bragg reflector structure, the wavelengths of the visible light and infrared reflection bands can be blue-shifted in tandem with the increase of the incident angle. This not only achieves a dynamic color gradient effect from light blue on the front to colorless on the side, enhancing the aesthetic appeal, but also enables the infrared blocking band to dynamically track and cover the region with the highest energy weight in the solar spectrum. This solves the problem of reduced heat insulation performance caused by fixed wavelengths when light is incident at an angle in traditional heat insulation films, achieving highly efficient and intelligent heat insulation with adaptive incident angle.

[0008] Optionally, the first resin material is polymethyl methacrylate (PMMA), and the second resin material is polyethylene terephthalate (PET).

[0009] Optionally, the refractive indices of the first resin material and the second resin material satisfy the following relationship: 0.1 ≤ (n H -n L ) / n avg ≤0.2, where n H n represents the refractive index of the high-refractive-index resin. L n represents the refractive index of the low-refractive-index resin. avg denoted as the average refractive index of the two resins.

[0010] By adopting the above technical solution, the ratio of the refractive index difference between the two resins to the average refractive index is controlled between 0.1 and 0.2, which ensures that the optical layer obtains a sufficiently high reflectivity in the target wavelength band, while avoiding the generation of too many unnecessary secondary reflection peaks, thus optimizing the balance between optical performance and thermal insulation efficiency.

[0011] Optionally, the optical layer has a gradient thickness structure, and the physical period thickness variation rate of adjacent 10 layers along the thickness direction is not less than 1%.

[0012] By adopting the above technical solution, the optical layer adopts a gradient layer thickness design, which makes the Bragg reflection conditions at different depth interfaces shift in an orderly manner when the angle changes. This design can precisely control the blue shift behavior of the entire reflection band, ensuring that the infrared reflection band can continuously and fully cover the 900-1150nm high-weight solar energy band within the incident angle range of 0° to 60°, thereby maximizing the angle of heat insulation performance.

[0013] Optionally, the absorbent layer includes a polymer matrix and ceramic insulating particles dispersed in the polymer matrix.

[0014] Optionally, the polymer matrix is ​​ethylene 2,5-furandicarboxylate (PEF) resin, the ceramic heat insulation particles are indium tin oxide (ITO) particles, and the particle size of the ceramic heat insulation particles is 30-50 nm.

[0015] By adopting the above technical solution and using PEF resin as the absorber layer matrix, its excellent water and oxygen barrier properties provide long-term protection for the internal ceramic particles, greatly reducing the performance degradation caused by water vapor erosion. At the same time, by controlling the particle size of ceramic particles to 30-50nm, it is possible to ensure high infrared absorption rate while effectively avoiding light scattering caused by excessively large particles, thus maintaining the high transmittance and low haze of the film.

[0016] Optionally, the protective layer is made of ethylene 2,5-furandicarboxylate (PEF) resin.

[0017] Optionally, the thickness of the protective layer is 3-5 μm, and the thickness of the absorbent layer is 3-5 μm.

[0018] Secondly, this application provides a method for preparing an incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection, using the following technical solution: A method for preparing an incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection includes the following steps: Q1. The first resin material and the second resin material used to form the optical layer are melted separately and then alternately stacked through a casting distributor to form a prefabricated multilayer optical film preform. Q2. The third resin material used to form the protective layer, the pre-made multilayer optical film preform, and the fourth resin material used to form the absorption layer are simultaneously introduced into the three-layer co-extrusion die. Q3. The three layers of material are combined in the die head and co-extruded onto the cooling roller to form a composite film preform; Q4. The composite membrane preform is subjected to biaxial stretching to obtain the heat-insulating composite membrane. Optionally, the fourth resin material is a polymer composite material containing ceramic heat-insulating particles; in step Q2, the pre-fabricated multilayer optical film preform, the third resin material, and the fourth resin material converge from the middle flow channel, the first side flow channel, and the second side flow channel of the die head, respectively, so that the absorption layer is located on the side of the optical layer facing away from the protective layer.

[0019] In summary, this application includes at least one of the following beneficial technical effects: 1. By utilizing the angle sensitivity of the Bragg reflection structure, the wavelengths of the visible light and infrared reflection bands can be blue-shifted in tandem with the increase of the incident angle. This not only achieves a dynamic color gradient effect from light blue on the front to colorless on the side, improving the aesthetic appeal, but also enables the infrared blocking band to dynamically track and cover the region with the highest energy weight in the solar spectrum. This solves the problem of reduced heat insulation performance caused by fixed wavelength when light is incident at an angle in traditional heat insulation films, and achieves highly efficient and intelligent heat insulation with adaptive incident angle. 2. The optical layer adopts a gradient layer thickness design, which makes the Bragg reflection conditions at different depth interfaces shift in an orderly manner when the angle changes. This design can precisely control the blue shift behavior of the entire reflection band, ensuring that the infrared reflection band can continuously and fully cover the 900-1150nm high solar energy band within the incident angle range of 0° to 60°, thereby maximizing the angle of heat insulation performance. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the extrusion channel in Example 1.

[0021] Figure 2 This is a diagram of the membrane structure of the incident angle adaptive dual-band thermal insulation composite membrane based on Bragg reflection in Example 1. Detailed Implementation

[0022] Preparation Example Preparation Example 1 Weigh 150g of ITO nanoparticles with an average particle size of 40nm and 2.25g of stearic acid, place them in 500ml of ethanol, ultrasonically disperse for 30 minutes, and then dry at 80℃ to obtain surface-modified ITO powder. Under ambient humidity ≤30%, 1000g of PEF resin particles, 10g of surface-modified ITO powder and 1g of compatibilizer polyethylene oxide were placed in a high-speed mixer and mixed at 1000rpm for 10 minutes to obtain a premix. The premixed material was fed into a twin-screw extruder (length-to-diameter ratio L / D=40) for melt blending. The temperatures of each section of the extruder were set as follows: feed section 235℃, melt section 250℃, and die section 258℃. The screw assembly used high-shear elements to ensure that the dispersed phase particle size was ≤100nm. After water cooling, stretching, and pelletizing, primary masterbatch with a particle size of 2-3mm was obtained. The primary masterbatch is vacuum dried at 60°C for 4 hours to reduce its moisture content to ≤500ppm, thus obtaining A-PEF resin masterbatch, in which the ITO powder content is approximately 13wt%.

[0023] Preparation Example 2 The difference between Preparation Example 2 and Preparation Example 1 is that PET particles of equal mass are used instead of PEF resin particles to prepare A-PET resin masterbatch.

[0024] Example

[0025] Example 1

[0026] This embodiment prepares a composite film of PEF protective layer / (PET-PMMA) optical layer / PEF absorption layer.

[0027] Melt PET resin and PMMA resin separately, as per [reference]. Figure 1 The first resin material, PET resin, is added to the S1 channel, and the second resin material, PMMA resin, is added to the S2 channel. Then, they are independently fed into the casting distributor and stacked alternately for 200 layers to form a multi-layered preform. The multi-layered preform then enters the middle channel P1 of the three-layer co-extrusion die. Molten PEF resin for the protective layer is added to the P2 channel of the die, and molten PEF resin for the absorbent layer is added to the P3 channel of the die. The resins in the P1, P2, and P3 channels converge in the die and flow out of the die, co-extruding and casting onto the chilling roller to form an unstretched thick sheet with a PEF / (PET-PMMA) / PEF layered structure. The above-mentioned thick sheet is biaxially stretched to complete the orientation and film formation: Longitudinal stretching: at a temperature of 82-85℃, stretch 3.5-3.8 times along the machine direction; Lateral stretching: at a temperature of 120-125℃, stretch 3.5-3.8 times along the direction perpendicular to the machine.

[0028] After stretching, the protective layer has a thickness of 4 μm, the absorbent layer has a thickness of 3 μm, and the refractive index n of the first resin material is... H The refractive index n of the second resin material is approximately 1.68. L Approximately 1.49, (n H -n L ) / n avg It is approximately 0.12, which meets the high reflectivity and bandwidth required by the optical layer.

[0029] The optical layer has a total of 200 layers arranged in an alternating AB pattern with a linearly varying thickness. The PET layer is layer A, and the PMMA layer is layer B. The physical thickness of each AB cycle increases continuously from the side closer to the protective layer to the side closer to the absorption layer. Within the same cycle, the ratio of the physical thickness of layer A to layer B is 1.12:1. The total thickness of the first five cycles (layers 1-10) is 1.58 μm, and the total thickness of the last five cycles (layers 191-200) is 1.94 μm.

[0030] Testing revealed that the optical layer exhibits 95% reflectivity in the 380-450nm and 1100-1350nm ranges, with a total solar infrared rejection rate of 42% and a total solar energy rejection rate of 35%. After 4000 hours of QUV aging, the total solar infrared rejection rate remained at 40% and the total solar energy rejection rate at 34%. The extremely low degradation in the optical layer's rejection performance indicates that the optical structure protected by the PEF layer possesses excellent durability.

[0031] Using a UV-Vis-NIR spectrophotometer equipped with a variable angle measurement accessory (VAS), the reflectance spectra were measured in the wavelength range of 300-2500 nm at incident angles (θ) of 0° and 60°. The incident angle was defined as the angle between the incident ray and the normal to the film surface. At 0°, the center wavelength λ of the first reflection band was measured. vis (0°) = 450nm, center wavelength λ of the second reflection band IR (0°) = 1350nm, and λ is measured at 60°. vis (60°) = 380 nm, λ IR (60°) = 1150nm, Δλ vis =λ vis (0°)-λ vis (60°)=450nm-380nm=70nm; Δλ IR =λ IR (0°)-λ IR (60°) = 1350nm - 1150nm = 200nm. The total angular change Δθ = 60°, Δλvis / Δθ=70nm / 60°≈1.17nm / °, Δλ IR / Δθ=200nm / 60°≈3.33nm / °.

[0032] Example 2

[0033] This embodiment prepares a composite film of PEF protective layer / (PET-PMMA) optical layer / A-PEF absorption layer.

[0034] The difference between Example 2 and Example 1 is that the material of the absorbent layer is the A-PEF resin masterbatch prepared in Example 1, that is, molten A-PEF resin is added into the P3 channel, the thickness of the protective layer is 3 μm, and the thickness of the absorbent layer is 5 μm.

[0035] Testing revealed that the optical layer exhibits 95% reflectivity in the 380-450nm and 1100-1350nm ranges, with a total solar infrared rejection rate of 78% and a total solar energy rejection rate of 58%. After 4000 hours of QUV aging, the total solar infrared rejection rate remained at 77% and the total solar energy rejection rate at 57%. This demonstrates that incorporating the ceramic absorber ITO into the PEF resin significantly improves the total solar infrared rejection rate and the total solar energy rejection rate of the composite film. Furthermore, due to the excellent oxygen and water barrier properties of PEF, the barrier properties of the ceramic slurry are virtually unaffected by external factors.

[0036] Example 3

[0037] This embodiment prepares a composite film of PET protective layer / (PET-PMMA) optical layer / A-PET absorption layer.

[0038] The difference between Example 3 and Example 1 is that the material of the protective layer is PET, and the material of the absorbent layer is the A-PET resin masterbatch obtained in Preparation Example 2. That is, molten PET resin is added into the P2 channel and molten A-PET resin is added into the P3 channel. The thickness of the protective layer is 5 μm and the thickness of the absorbent layer is 4 μm.

[0039] Testing revealed that the optical layer exhibited 95% reflectivity in the 380-450nm and 1100-1350nm ranges, with a total solar infrared rejection rate of 77% and a total solar energy rejection rate of 56%. After 4000 hours of QUV aging, the total solar infrared rejection rate was 59% and the total solar energy rejection rate was 50%. This indicates that because PET has lower oxygen and water barrier properties than PEF, even when the protective and absorber layers are replaced with PET, the initial barrier effect of the film remains high. However, after 4000 hours of QUV aging, the solar infrared rejection rate and total rejection rate significantly decreased, demonstrating that the barrier effect of the protective and absorber layer materials greatly influences the degradation of the ceramic absorbent.

[0040] Example 4

[0041] This embodiment prepares a composite film of A-PEF protective layer / (PET-PMMA) optical layer / PEF absorption layer.

[0042] The difference between Example 4 and Example 2 is that the materials of the protective layer and the absorbent layer are interchanged, that is, molten A-PEF resin is added into the P2 channel and molten PEF resin is added into the P3 channel.

[0043] A-PEF resin containing infrared absorbers was placed as the first layer, and PEF without absorbers was placed as the bottom layer. In this way, light first passes through the A-PEF absorption layer and then through the optical layer. The optical layer was tested and found to have a reflectivity of 95% in the 380-450nm and 1100-1350nm ranges, a total solar infrared rejection rate of 74%, and a total solar energy rejection rate of 56%. After 4000 hours of QUV aging, the total solar infrared rejection rate was 62% and the total solar energy rejection rate was 50%.

[0044] It can be seen that the solar energy rejection rate has decreased slightly. This is related to the rejection mechanism. After 4000 hours of QUV aging, the solar energy rejection rate is severely reduced because the absorbent is located in the outer PEF layer. This is because the ceramic absorbent in the PEF is greatly corroded by water vapor, resulting in a severe degradation of the absorbent's performance.

[0045] Comparative Example Comparative Example 1 Ceramic heat insulation film (commercially available) is made by coating a layer of ceramic heat insulation paste onto a PET base film.

[0046] Comparative Example 2 Silver-plated heat insulation film (commercially available) is made by coating a layer of silver onto a PET base film using magnetron sputtering.

[0047] The optical performance test results of Examples 1-4 and Comparative Examples 1-2 in solar energy sources are shown in Table 1 below: Table 1. Optical performance test results of Examples 1-4 and Comparative Examples 1-2 in solar light sources.

[0048] Based on Examples 1-4 and Comparative Examples 1-2, and in conjunction with Table 1, it can be seen that the PEF / (PET-PMMA) / A-PEF composite film prepared in Example 2 has the best barrier properties. In contrast, the ceramic heat insulation films of Comparative Examples 1 and 2 prepared by coating showed significant degradation in the QUV anti-aging test, indicating that the greater the protective effect on the ceramic slurry, the lower the performance degradation of the heat insulation film.

[0049] The optical performance test results of Examples 1-2 in solar light sources are shown in Table 2 below: Table 2. Optical performance test results of Examples 1-2 in solar light sources

[0050] As can be seen from Examples 1-2 and Table 2, as the incident angle increases, the visible light transmittance of the heat insulation film increases slightly, while the infrared blocking rate and total blocking rate of solar energy increase significantly. The addition of ceramic slurry will reduce the light transmittance of the heat insulation film to a certain extent, but will significantly increase the blocking performance of the heat insulation film. While maintaining a high light transmittance, it gives the composite film an angle-dependent appearance color change.

[0051] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A dual-band thermal insulation composite film with incident angle adaptive based on Bragg reflection, characterized in that: It includes a protective layer, an optical layer and an absorption layer arranged sequentially. The optical layer is formed by alternating stacking of a first resin material and a second resin material, with a stacking number of not less than 100 layers. The first resin material and the second resin material have different refractive indices, so as to form a first reflection band in the 360-450nm band and a second reflection band in the 1100-1350nm band under vertical incident conditions. The reflected wavelength of the heat-insulating composite film undergoes a blue shift as the incident angle increases, and satisfies: Δλ vis / Δθ≥1nm / °,Δλ IR / Δθ≥3 nm / °, where Δλ vis Δλ is the wavelength change of the first reflection band. IR Δθ represents the wavelength change of the second reflection zone, and Δθ represents the change of the incident angle.

2. The incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection according to claim 1, characterized in that: The first resin material is polymethyl methacrylate (PMMA), and the second resin material is polyethylene terephthalate (PET).

3. The incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection according to claim 1, characterized in that, The refractive indices of the first resin material and the second resin material satisfy the following relationship: 0.1 ≤ (n H -n L ) / n avg ≤0.2, where n H n represents the refractive index of the high-refractive-index resin. L n represents the refractive index of the low-refractive-index resin. avg denoted as the average refractive index of the two resins.

4. The incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection according to claim 1, characterized in that: The optical layer has a gradient thickness structure, and the physical period thickness variation rate of adjacent 10 layers along the thickness direction is not less than 1%.

5. The incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection according to claim 1, characterized in that: The absorbent layer comprises a polymer matrix and ceramic insulating particles dispersed in the polymer matrix.

6. The incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection according to claim 5, characterized in that: The polymer matrix is ​​ethylene 2,5-furandicarboxylate (PEF) resin, the ceramic heat insulation particles are indium tin oxide (ITO) particles, and the particle size of the ceramic heat insulation particles is 30-50 nm.

7. The incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection according to claim 1, characterized in that: The protective layer is made of ethylene 2,5-furandicarboxylate (PEF) resin.

8. The incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection according to claim 1, characterized in that: The thickness of the protective layer is 3-5 μm, and the thickness of the absorbent layer is 3-5 μm.

9. The method for preparing the incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection as described in any one of claims 1-8, characterized in that, Includes the following steps: Q1. The first resin material and the second resin material used to form the optical layer are melted separately and then alternately stacked through a casting distributor to form a prefabricated multilayer optical film preform. Q2. The third resin material used to form the protective layer, the pre-made multilayer optical film preform, and the fourth resin material used to form the absorption layer are simultaneously introduced into the three-layer co-extrusion die. Q3. The three layers of material are combined in the die head and co-extruded onto the cooling roller to form a composite film preform; Q4. The composite membrane preform is subjected to biaxial stretching to obtain the heat-insulating composite membrane.

10. The method for preparing the incident angle adaptive dual-band thermal insulation composite film based on Bragg reflection according to claim 9, characterized in that: The fourth resin material is a polymer composite material containing ceramic heat-insulating particles; in step Q2, the pre-fabricated multilayer optical film preform, the third resin material, and the fourth resin material converge from the middle flow channel, the first side flow channel, and the second side flow channel of the die head, respectively, so that the absorption layer is located on the side of the optical layer facing away from the protective layer.

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